When photosensitive material is processed in a processing tank using current photographic processors, squeegees are typically used to remove as much of the processing surface liquid as possible to avoid contamination at the next processing tank. In some cases, no effort is made to remove the processing surface liquid.
It is not common to apply a protective coating on a photosensitive material in a bath. In cases where a protective coating is applied to a photosensitive material, there is little attempt to control the specific laydown of the coating onto the surface of the photographic material. For example, U.S. Pat. No. 2,173,480 describes the concept of applying a protective coating, however, in this document there is no concern about controlling the specific laydown amount of the coating material applied.
Currently, in order to apply a solution to the surface of a web in uniform layer amounts, it is necessary that it be done in manufacturing under very controlled conditions and temperature. In the past, this has been difficult to do in minilab or traditional lab photographic processing environment as an integral part of the process.
In order to apply a protective coating to an emulsion surface of a photosensitive material, control over the thickness, uniformity and laydown amount of the layer being applied is needed in order to provide for adequate protection against moisture and scratches. The control is needed for several reasons: 1) the protective coating must be applied in a manner that insures that the surface is uniformly coated so that the coating can provide adequate protection to the entire surface; 2) the thickness of the coating must be controlled because if the coating is too thick, it could cause cracking due a non-uniform drying; 3) a thick coating could dull the surface and the underlying image; and 4) the coating solutions can be of different viscosities. Conventional methods of immersing the photosensitive materials into a bath and squeegeeing off the excess liquid will not provide for a uniform protective coating and may produce too thin a coating which would provide inadequate protection.